How to search column after applying valuePrepareFunction()

For example if one of the column in my schema has following definition:

```
flag: {
title: 'Flag',
type: 'string',
valuePrepareFunction: (value) => {
return (value === true) ? 'On' : 'Off';
}
},
```
I can search the column by "true" or "false" but NOT by "On" or "Off". Is there way I can override search/filter logic so I can search by the transformed value of the column data?

I looked in documentation and I see we have "filterFunction" property but not sure how it can be used in my case? Thanks